Interconnect bumps are used primarily to make electrical connections between connectors and circuit boards. The interconnect bumps make electrical contact above the connector or board with another electrical component which could be either another connector or a circuit board. In a connector employing a densely-packed interconnect pattern the height of interconnect bumps is critical to avoid cross-talk and other unwanted electrical phenomenon associated with such patterns on electrical connectors.
The standard process to form interconnect bumps is an additive process in which the circuit traces and bumps are formed by depositing successive layers of metal on a suitable substrate by electrodeposition, sputtering, vapor deposition or other known processes. Bumps formed by this additive process are typically 0.001 to 0.0015 inches (2.54.times.10.sup.-5 to 3.81.times.10.sup.-5 meters) high and do not have any mechanical anchoring or support features other than adhesion between the layers.
The lack of height makes connectors employing such bumps in densely-packed interconnect patterns subject to cross-talk and other unwanted electrical phenomenon. The height is limited primarily by the structure of the bumps themselves, as well as the processes used to form the interconnect bumps. Attempts to form higher bumps results in bumps which delaminate or "slide" off their base structures. Once the bumps delaminate, the connectors fail to make electrical connection between their associated components.
Prior art processes used to form interconnect bumps also include etching a single layer or series of layers which were previously built up on an electrical component. Such a method is described in U.S. Pat. No. 4,357,750 to Ostman, issued Nov. 9, 1982. These methods typically start with a very thick layer of copper and use standard photolithographic methods to define the desired pattern. Typically an ammoniacal etchant is used to etch away undesired copper to form the pattern. The disadvantages to this process are the high cost of depositing a large amount of copper and then removing it in a process from which the copper may or may not be recovered. In addition, the thick electrodeposited copper base material is not suitable for dynamic flex circuit applications because it lacks flexibility, it is difficult to form bumps with straight side walls because of the etching process, and the process is not well-suited for the fabrication of highly complex, very high density printed circuits.
To solve the above-mentioned problems and others not mentioned, the present method and apparatus provide a stable, reliable interconnect bump for use on connectors having high density interconnect patterns.